Optical communication systems are desirable because of the wide bandwidths available for the information signal channels. In general, there is a direct trade off between increased bandwidth capabilities and vulnerability to large scale channel disruption by transmission medium failure. The robustness of an optical fiber is increasingly important with increasing bandwidth capability.
Signals fade with distance while traveling through any type of cable. The greater the distance the fainter the signal becomes. When a digital signal fades the bit error rate rises rapidly. When an analog signal fades it becomes distorted or noisy. Communication system utilize amplifiers or repeaters coupled to the cables to overcome this problem.
Lightwave repeaters, regenerators and optical amplifiers extend transmission distances of light signals. Inserted into a fiber system at a point where the original light signal becomes weak, they generate a stronger signal, effectively extending the operating distances. Repeaters and regenerators convert the light signal into an electrical signal before amplifying the signal. Optical amplifiers directly amplify the light signal. It is desirable to hermetically seal the repeaters, regenerators, optical amplifiers and other devices within a housing to prevent deterioration due to atmospheric conditions. This is particularly necessary for buried terrestrial or submarine optical fiber systems. The fact that the optical fiber cores have a very small diameter (typically 8 to 9 .mu.m) makes them susceptible to damage and difficult to handle.
U.S. Pat. No. 4,119,363, entitled "Package For Optical Devices Including Optical Fiber-To-Metal Hermetic Seal", issued on Oct. 10, 1978 to Irfan Camlibel et al, discloses an optical fiber that is hermetically sealed to a metal housing, where solder filling a thin walled metal tube forms a hermetic seal. The end of the optical fiber that is inserted into the tube is stripped to the bare optical fiber.
U.S. Pat. No. 4,699,456, entitled "Hermetic Fiber Seal", issued on Oct. 13, 1987 to Donald R. Mackenzie, discloses an assembly for hermetically sealing and aligning optical fibers. An end of the optical fiber is stripped to the bare optical fiber before inserting into the device. Pressure from a flange onto a gold ring forms the hermetic seal.
He absorption by Teflon RF connectors and optical fiber jacketing poses a difficulty in leak testing a hermetic seal to a LiNbO.sub.3 package. The present commercial practice that is used to address this problem involves drilling a hole through the lid prior to plating. Reflux solder is melted on the lid surface, after sealing, to create a closure. This may be used to allow outgassing of the package and not be used to test for hermeticity. Additionally, there has been used a crimp tube attached to the package which is then pinched off to create a closure.
Therefore, there is a need for an inexpensive and reliable way to leak test and create a hermetic seal to a LiNbO.sub.3 package.